This invention relates to a magnetic rotor impeller and more particularly to a floating impeller assembly for use with an electromagnetic unit for drawing aquarium water into an aquarium filter for the purpose of filtration of contaminated aquarium water.
The prior art related to magnetic rotor assemblies includes U.S. Pat. Nos. 4,512,885 and 4,861,468 and a unit which incorporates a snap-fit assembly.
In U.S. Pat. No. 4,512,885 there is described an external aquarium filter which includes a rotor magnetically coupled to an electromagnetic stator unit. An impeller is mounted with respect to the rotor for driving engagement by the rotor. In such aforementioned patent, the electromagnetic stator unit is removably coupled to the filter housing and includes a well hermetically separated from the stator stack. The rotor is part of an assembly which comprises a shaft which is fixed with respect to the stator unit. The rotor is rotatingly positioned on the shaft. A magnet is insert molded onto the rotor. The impeller is likewise rotatingly mounted onto the shaft and is operatively connected to be driven by the rotor. The electromagnetic stator unit creates a flux which is cut by the magnet to cause the rotor to rotate upon the shaft and drive the impeller. The impeller creates a reduced pressure which draws the aquarium water into the filter housing for filtration and aeration.
The rotor assembly in the aforementioned patent forms a single unitary assembly including the shaft, the rotor, the magnet mounted onto the rotor, and the impeller. A washer is mounted onto the shaft in order to accommodate thrust forces which are generated by the assembly and reduce noise caused by rubbing of the impeller against the plugs. The plugs are placed at opposing ends of the shaft to fix it in position with one end seated into the well and the other end fixed into an appropriate seat provided in the intake tube.
In U.S. Pat. No. 4,861,468 there is described a rotor impeller assembly which includes a shaft with a magnetic rotor rotationally mounted onto the shaft. An impeller coupled onto a sleeve is also rotationally mounted with respect to the shaft. A clutch mechanism is provided on the inside of the sleeve between the magnetic rotor and the impeller sleeve which rotationally drives the impeller by means of the rotation of the magnetic rotor. A thrust washer is placed on the shaft to accommodate thrust forces generated by the assembly and to reduce the noise caused by rubbing of the impeller against the plugs.
In an additional rotor impeller which is part of the prior art the rotor is mounted onto a shaft with the rotor extended beyond the magnet portion. The impeller, again coupled to a sleeve, and the rotor are assembled by moving them axially toward each other until the impeller sleeve covers a portion of the extended rotor and the geometry of the impeller sleeve flexes and the impeller sleeve snaps onto the extended portion of the rotor. A clutch mechanism, likewise, is provided on the inside of the sleeve. This assembly requires the achievement and maintenance of tight tolerances in the engagement geometry of the two parts in order to accomplish the snap-fit assembly. The maintenance of these tight tolerances requires time consuming and costly procedures during the fabrication of molds for the component parts and costly quality control procedures for every production run. Additional disadvantages of this construction include the need for the extended rotor unit to accommodate the snap-on sleeve of the impeller. This extended rotor results in difficulty in molding due to post molding distortion; i.e., bowing of parts which results in problems in maintaining accurately the coaxial rotation of the rotor.
Both types of prior art impeller assemblies have wide sleeves supporting the impeller with the clutch mechanism inside the sleeve. This large projected area of the impeller assembly just below the impeller blades causes a lift of the impeller assembly. The lifting of the assembly causes the assembly to rub against the support structure resulting in the generation of friction, wear, and objectionable noise.